With the occurrence of telecommunication networks and in particular due to the huge spreading of multimedia data-capable personal computers and, most recently, of so-called solid state players, a need has arisen to market digital multimedia data, such as digital audio data and/or digital video data, commercially. Telecommunication networks for example can be analog telephone lines, digital telephone lines, such as ISDN, or the Internet. Among the commercial providers of multimedia products there is a need to sell or lend multimedia data, wherein it should be possible for a costumer to be able to select a certain product individually at any time from a certain catalogue, this product then of course being only allowed to be used by the costumer who has paid for it.
Unlike well-known encrypted television programs, such as the television channel Premiere, in which the emitted data is encrypted in the same way for all users who have acquired a suitable decryption device by paying a certain charge, the present invention is to provide methods and devices enabling an individual, customer-selective and safe encryption and decryption of multimedia data. Unlike the television channels mentioned above which give a fixed program all of which the user has to decide for, the methods and devices of the present invention enable a maximum freedom of selection for the user, which means that the user has only to pay for those products he or she actually wants to use.
DE 196 25 635 C1 describes methods and devices for encrypting and decrypting multimedia data, the multimedia data being present in the form of an encrypted multimedia file comprising a destination data block and a payload data block. Parts of the destination data block and at least some parts of the payload data block are encrypted by means of different keys, especially symmetrical encryption methods being used.
Further, in the method for encrypting or decrypting multimedia data described in DE 196 256 35 C1 a user index is entered into a determination data block of a bitstream with encrypted multimedia data that identifies the user authorized to use an encrypted multimedia data stream. If this user index identifies merely one person, this method is only safe against unauthorized copying if that person who has purchased an encrypted multimedia data stream acts correctly and legally. This can, however, not always be guaranteed. If the person who has purchased an encrypted multimedia data stream legally carries out copying, it will not be possible to see from a copy who has copied it. The origin of the copy can therefore not be tracked down anymore which will open the way for violations of copyrights, incorrect behaviour assumed.
However, if the user index does, not only identify the user as a person but a specific player of a user, like e.g. the PC of the user, a safety is achieved in such a way that the user can play the encrypted multimedia data stream only on the player identified by the user index regardless whether the user behaves legally or illegally.
However, the problem with this solution is the fact that it is not flexible, i.e. it dictates the user where he has to play the purchased multimedia data stream due to the copyright protection. There is not a lot of imagination needed to predict that such system will only find little acceptance at the market especially when thinking about the fact that a number of players exist in a normal household. Such players can include for example a personal computer, a laptop, a hifi system, a car hifi system, a video recorder, a solid state player, etc.